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/**
 * @file control.cpp
 * Control functions for ekf attitude and position estimator.
 *
 * @author Paul Riseborough <p_riseborough@live.com.au>
 *
 */

#include "../ecl.h"
#include "ekf.h"
#include <mathlib/mathlib.h>

void Ekf::controlFusionModes()
{
	// Store the status to enable change detection
	_control_status_prev.value = _control_status.value;

	// monitor the tilt alignment
	if (!_control_status.flags.tilt_align) {
		// whilst we are aligning the tilt, monitor the variances
		const Vector3f angle_err_var_vec = calcRotVecVariances();

		// Once the tilt variances have reduced to equivalent of 3deg uncertainty, re-set the yaw and magnetic field states
		// and declare the tilt alignment complete
		if ((angle_err_var_vec(0) + angle_err_var_vec(1)) < sq(math::radians(3.0f))) {
			_control_status.flags.tilt_align = true;
			_control_status.flags.yaw_align = resetMagHeading(_mag_lpf.getState()); // TODO: is this needed?

			// send alignment status message to the console
			const char* height_source = nullptr;
			if (_control_status.flags.baro_hgt) {
				height_source = "baro";

			} else if (_control_status.flags.ev_hgt) {
				height_source = "ev";

			} else if (_control_status.flags.gps_hgt) {
				height_source = "gps";

			} else if (_control_status.flags.rng_hgt) {
				height_source = "rng";

			} else {
				height_source = "unknown";

			}
			if(height_source){
				ECL_INFO("%llu: EKF aligned, (%s hgt, IMU buf: %i, OBS buf: %i)",
					(unsigned long long)_imu_sample_delayed.time_us, height_source, (int)_imu_buffer_length, (int)_obs_buffer_length);
			}
		}
	}

	// check for intermittent data (before pop_first_older_than)
	const baroSample &baro_init = _baro_buffer.get_newest();
	_baro_hgt_faulty = !isRecent(baro_init.time_us, 2 * BARO_MAX_INTERVAL);

	const gpsSample &gps_init = _gps_buffer.get_newest();
	_gps_hgt_intermittent = !isRecent(gps_init.time_us, 2 * GPS_MAX_INTERVAL);

	// check for arrival of new sensor data at the fusion time horizon
	_time_prev_gps_us = _gps_sample_delayed.time_us;
	_gps_data_ready = _gps_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_gps_sample_delayed);
	_mag_data_ready = _mag_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_mag_sample_delayed);

	if (_mag_data_ready) {
		// if enabled, use knowledge of theoretical magnetic field vector to calculate a synthetic magnetomter Z component value.
		// this is useful if there is a lot of interference on the sensor measurement.
		if (_params.synthesize_mag_z && (_params.mag_declination_source & MASK_USE_GEO_DECL) &&_NED_origin_initialised) {
			const Vector3f mag_earth_pred = Dcmf(Eulerf(0, -_mag_inclination_gps, _mag_declination_gps)) * Vector3f(_mag_strength_gps, 0, 0);
			_mag_sample_delayed.mag(2) = calculate_synthetic_mag_z_measurement(_mag_sample_delayed.mag, mag_earth_pred);
			_control_status.flags.synthetic_mag_z = true;
		} else {
			_control_status.flags.synthetic_mag_z = false;
		}
	}

	_delta_time_baro_us = _baro_sample_delayed.time_us;
	_baro_data_ready = _baro_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_baro_sample_delayed);

	// if we have a new baro sample save the delta time between this sample and the last sample which is
	// used below for baro offset calculations
	if (_baro_data_ready) {
		_delta_time_baro_us = _baro_sample_delayed.time_us - _delta_time_baro_us;
	}



	{
	// Get range data from buffer and check validity
	const bool is_rng_data_ready = _range_buffer.pop_first_older_than(_imu_sample_delayed.time_us, _range_sensor.getSampleAddress());
	_range_sensor.setDataReadiness(is_rng_data_ready);
	_range_sensor.runChecks(_imu_sample_delayed.time_us, _R_to_earth);

	// update range sensor angle parameters in case they have changed
	_range_sensor.setPitchOffset(_params.rng_sens_pitch);
	_range_sensor.setCosMaxTilt(_params.range_cos_max_tilt);
	}

	if (_range_sensor.isDataHealthy()) {
		// correct the range data for position offset relative to the IMU
		Vector3f pos_offset_body = _params.rng_pos_body - _params.imu_pos_body;
		Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
		_range_sensor.setRange(_range_sensor.getRange() + pos_offset_earth(2) / _range_sensor.getCosTilt());
	}

	// We don't fuse flow data immediately because we have to wait for the mid integration point to fall behind the fusion time horizon.
	// This means we stop looking for new data until the old data has been fused, unless we are not fusing optical flow,
	// in this case we need to empty the buffer
	if (!_flow_data_ready || !_control_status.flags.opt_flow) {
		_flow_data_ready = _flow_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_flow_sample_delayed)
				   && (_R_to_earth(2, 2) > _params.range_cos_max_tilt);
	}

	// check if we should fuse flow data for terrain estimation
	if (!_flow_for_terrain_data_ready && _flow_data_ready && _control_status.flags.in_air) {
		// only fuse flow for terrain if range data hasn't been fused for 5 seconds
		_flow_for_terrain_data_ready = isTimedOut(_time_last_hagl_fuse, (uint64_t)5E6);
		// only fuse flow for terrain if the main filter is not fusing flow and we are using gps
		_flow_for_terrain_data_ready &= (!_control_status.flags.opt_flow && _control_status.flags.gps);
	}

	_ev_data_ready = _ext_vision_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_ev_sample_delayed);
	_tas_data_ready = _airspeed_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_airspeed_sample_delayed);

	// check for height sensor timeouts and reset and change sensor if necessary
	controlHeightSensorTimeouts();

	// control use of observations for aiding
	controlMagFusion();
	controlOpticalFlowFusion();
	controlGpsFusion();
	controlAirDataFusion();
	controlBetaFusion();
	controlDragFusion();
	controlHeightFusion();

	// Additional data odoemtery data from an external estimator can be fused.
	controlExternalVisionFusion();

	// Additional horizontal velocity data from an auxiliary sensor can be fused
	controlAuxVelFusion();

	// Fake position measurement for constraining drift when no other velocity or position measurements
	controlFakePosFusion();

	// check if we are no longer fusing measurements that directly constrain velocity drift
	update_deadreckoning_status();
}

void Ekf::controlExternalVisionFusion()
{
	// Check for new external vision data
	if (_ev_data_ready) {

		// if the ev data is not in a NED reference frame, then the transformation between EV and EKF navigation frames
		// needs to be calculated and the observations rotated into the EKF frame of reference
		if ((_params.fusion_mode & MASK_ROTATE_EV) && ((_params.fusion_mode & MASK_USE_EVPOS) || (_params.fusion_mode & MASK_USE_EVVEL)) && !_control_status.flags.ev_yaw) {
			// rotate EV measurements into the EKF Navigation frame
			calcExtVisRotMat();
		}

		// external vision aiding selection logic
		if (_control_status.flags.tilt_align && _control_status.flags.yaw_align) {

			// check for a external vision measurement that has fallen behind the fusion time horizon
			if (isRecent(_time_last_ext_vision, 2 * EV_MAX_INTERVAL)) {
				// turn on use of external vision measurements for position
				if (_params.fusion_mode & MASK_USE_EVPOS && !_control_status.flags.ev_pos) {
					_control_status.flags.ev_pos = true;
					resetHorizontalPosition();
					ECL_INFO_TIMESTAMPED("starting vision pos fusion");
				}

				// turn on use of external vision measurements for velocity
				if (_params.fusion_mode & MASK_USE_EVVEL && !_control_status.flags.ev_vel) {
					_control_status.flags.ev_vel = true;
					resetVelocity();
					ECL_INFO_TIMESTAMPED("starting vision vel fusion");
				}
			}
		}

		// external vision yaw aiding selection logic
		if (!_control_status.flags.gps && (_params.fusion_mode & MASK_USE_EVYAW) && !_control_status.flags.ev_yaw && _control_status.flags.tilt_align) {
			// don't start using EV data unless data is arriving frequently
			if (isRecent(_time_last_ext_vision, 2 * EV_MAX_INTERVAL)) {
				// reset the yaw angle to the value from the vision quaternion
				const Eulerf euler_obs(_ev_sample_delayed.quat);
				const float yaw = euler_obs(2);
				const float yaw_variance = fmaxf(_ev_sample_delayed.angVar, sq(1.0e-2f));

				resetQuatStateYaw(yaw, yaw_variance, true);

				// flag the yaw as aligned
				_control_status.flags.yaw_align = true;

				// turn on fusion of external vision yaw measurements and disable all magnetometer fusion
				_control_status.flags.ev_yaw = true;
				_control_status.flags.mag_dec = false;

				stopMagHdgFusion();
				stopMag3DFusion();

				ECL_INFO_TIMESTAMPED("starting vision yaw fusion");
			}
		}



		// determine if we should use the horizontal position observations
		if (_control_status.flags.ev_pos) {

			Vector3f ev_pos_obs_var;
			Vector2f ev_pos_innov_gates;

			// correct position and height for offset relative to IMU
			const Vector3f pos_offset_body = _params.ev_pos_body - _params.imu_pos_body;
			const Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
			_ev_sample_delayed.pos -= pos_offset_earth;

			// Use an incremental position fusion method for EV position data if GPS is also used
			if (_params.fusion_mode & MASK_USE_GPS) {
				_fuse_hpos_as_odom = true;
			} else {
				_fuse_hpos_as_odom = false;
			}

			if (_fuse_hpos_as_odom) {
				if (!_hpos_prev_available) {
					// no previous observation available to calculate position change
					_hpos_prev_available = true;

				} else {
					// calculate the change in position since the last measurement
					Vector3f ev_delta_pos = _ev_sample_delayed.pos - _pos_meas_prev;

					// rotate measurement into body frame is required when fusing with GPS
					ev_delta_pos = _R_ev_to_ekf * ev_delta_pos;

					// use the change in position since the last measurement
					_ev_pos_innov(0) = _state.pos(0) - _hpos_pred_prev(0) - ev_delta_pos(0);
					_ev_pos_innov(1) = _state.pos(1) - _hpos_pred_prev(1) - ev_delta_pos(1);

					// observation 1-STD error, incremental pos observation is expected to have more uncertainty
					Matrix3f ev_pos_var = matrix::diag(_ev_sample_delayed.posVar);
					ev_pos_var = _R_ev_to_ekf * ev_pos_var * _R_ev_to_ekf.transpose();
					ev_pos_obs_var(0) = fmaxf(ev_pos_var(0, 0), sq(0.5f));
					ev_pos_obs_var(1) = fmaxf(ev_pos_var(1, 1), sq(0.5f));
				}

				// record observation and estimate for use next time
				_pos_meas_prev = _ev_sample_delayed.pos;
				_hpos_pred_prev = _state.pos.xy();

			} else {
				// use the absolute position
				Vector3f ev_pos_meas = _ev_sample_delayed.pos;
				Matrix3f ev_pos_var = matrix::diag(_ev_sample_delayed.posVar);
				if (_params.fusion_mode & MASK_ROTATE_EV) {
					ev_pos_meas = _R_ev_to_ekf * ev_pos_meas;
					ev_pos_var = _R_ev_to_ekf * ev_pos_var * _R_ev_to_ekf.transpose();
				}
				_ev_pos_innov(0) = _state.pos(0) - ev_pos_meas(0);
				_ev_pos_innov(1) = _state.pos(1) - ev_pos_meas(1);

				ev_pos_obs_var(0) = fmaxf(ev_pos_var(0, 0), sq(0.01f));
				ev_pos_obs_var(1) = fmaxf(ev_pos_var(1, 1), sq(0.01f));

				// check if we have been deadreckoning too long
				if (isTimedOut(_time_last_hor_pos_fuse, _params.reset_timeout_max)) {
					// only reset velocity if we have no another source of aiding constraining it
					if (isTimedOut(_time_last_of_fuse, (uint64_t)1E6) &&
					    isTimedOut(_time_last_hor_vel_fuse, (uint64_t)1E6)) {
						resetVelocity();
					}

					resetHorizontalPosition();
				}
			}

			// innovation gate size
			ev_pos_innov_gates(0) = fmaxf(_params.ev_pos_innov_gate, 1.0f);

			fuseHorizontalPosition(_ev_pos_innov, ev_pos_innov_gates, ev_pos_obs_var, _ev_pos_innov_var, _ev_pos_test_ratio);
		}

		// determine if we should use the velocity observations
		if (_control_status.flags.ev_vel) {

			Vector3f ev_vel_obs_var;
			Vector2f ev_vel_innov_gates;

			_ev_vel_innov = _state.vel - getVisionVelocityInEkfFrame();

			// check if we have been deadreckoning too long
			if (isTimedOut(_time_last_hor_vel_fuse, _params.reset_timeout_max)) {
				// only reset velocity if we have no another source of aiding constraining it
				if (isTimedOut(_time_last_of_fuse, (uint64_t)1E6) &&
				    isTimedOut(_time_last_hor_pos_fuse, (uint64_t)1E6)) {
					resetVelocity();
				}
			}

			ev_vel_obs_var = matrix::max(getVisionVelocityVarianceInEkfFrame(), sq(0.05f));

			ev_vel_innov_gates.setAll(fmaxf(_params.ev_vel_innov_gate, 1.0f));

			fuseHorizontalVelocity(_ev_vel_innov, ev_vel_innov_gates,ev_vel_obs_var, _ev_vel_innov_var, _ev_vel_test_ratio);
			fuseVerticalVelocity(_ev_vel_innov, ev_vel_innov_gates, ev_vel_obs_var, _ev_vel_innov_var, _ev_vel_test_ratio);
		}

		// determine if we should use the yaw observation
		if (_control_status.flags.ev_yaw) {
			fuseHeading();
		}

	} else if ((_control_status.flags.ev_pos || _control_status.flags.ev_vel)
		   && isTimedOut(_time_last_ext_vision, (uint64_t)_params.reset_timeout_max)) {

		// Turn off EV fusion mode if no data has been received
		stopEvFusion();
		ECL_INFO_TIMESTAMPED("vision data stopped");

	}
}

void Ekf::controlOpticalFlowFusion()
{
	// TODO: These motion checks run all the time. Pull them out of this function
	// Check if on ground motion is un-suitable for use of optical flow
	if (!_control_status.flags.in_air) {
		// When on ground check if the vehicle is being shaken or moved in a way that could cause a loss of navigation
		const float accel_norm = _accel_vec_filt.norm();

		const bool motion_is_excessive = ((accel_norm > (CONSTANTS_ONE_G * 1.5f)) // upper g limit
					    || (accel_norm < (CONSTANTS_ONE_G * 0.5f)) // lower g limit
					    || (_ang_rate_magnitude_filt > _flow_max_rate) // angular rate exceeds flow sensor limit
					    || (_R_to_earth(2,2) < cosf(math::radians(30.0f)))); // tilted excessively

		if (motion_is_excessive) {
			_time_bad_motion_us = _imu_sample_delayed.time_us;

		} else {
			_time_good_motion_us = _imu_sample_delayed.time_us;
		}

	} else {
		_time_bad_motion_us = 0;
		_time_good_motion_us = _imu_sample_delayed.time_us;
	}

	// Accumulate autopilot gyro data across the same time interval as the flow sensor
	_imu_del_ang_of += _imu_sample_delayed.delta_ang - _state.delta_ang_bias;
	_delta_time_of += _imu_sample_delayed.delta_ang_dt;

	// New optical flow data is available and is ready to be fused when the midpoint of the sample falls behind the fusion time horizon
	if (_flow_data_ready) {
		// Inhibit flow use if motion is un-suitable or we have good quality GPS
		// Apply hysteresis to prevent rapid mode switching
		float gps_err_norm_lim;
		if (_control_status.flags.opt_flow) {
			gps_err_norm_lim = 0.7f;
		} else {
			gps_err_norm_lim = 1.0f;
		}

		// Check if we are in-air and require optical flow to control position drift
		bool flow_required = _control_status.flags.in_air &&
				(_is_dead_reckoning // is doing inertial dead-reckoning so must constrain drift urgently
				  || (isOnlyActiveSourceOfHorizontalAiding(_control_status.flags.opt_flow))
				  || (_control_status.flags.gps && (_gps_error_norm > gps_err_norm_lim))); // is using GPS, but GPS is bad

		if (!_inhibit_flow_use && _control_status.flags.opt_flow) {
			// inhibit use of optical flow if motion is unsuitable and we are not reliant on it for flight navigation
			bool preflight_motion_not_ok = !_control_status.flags.in_air && ((_imu_sample_delayed.time_us - _time_good_motion_us) > (uint64_t)1E5);
			bool flight_motion_not_ok = _control_status.flags.in_air && !isTerrainEstimateValid();
			if ((preflight_motion_not_ok || flight_motion_not_ok) && !flow_required) {
				_inhibit_flow_use = true;
			}
		} else if (_inhibit_flow_use && !_control_status.flags.opt_flow){
			// allow use of optical flow if motion is suitable or we are reliant on it for flight navigation
			bool preflight_motion_ok = !_control_status.flags.in_air && ((_imu_sample_delayed.time_us - _time_bad_motion_us) > (uint64_t)5E6);
			bool flight_motion_ok = _control_status.flags.in_air && isRangeAidSuitable();
			if (preflight_motion_ok || flight_motion_ok || flow_required) {
				_inhibit_flow_use = false;
			}
		}

		// Handle cases where we are using optical flow but are no longer able to because data is old
		// or its use has been inhibited.
		if (_control_status.flags.opt_flow) {
			if (_inhibit_flow_use) {
				stopFlowFusion();
				_time_last_of_fuse = 0;

			} else if (isTimedOut(_time_last_of_fuse, (uint64_t)_params.reset_timeout_max)) {
				stopFlowFusion();
			}
		}

		// optical flow fusion mode selection logic
		if ((_params.fusion_mode & MASK_USE_OF) // optical flow has been selected by the user
			&& !_control_status.flags.opt_flow // we are not yet using flow data
			&& _control_status.flags.tilt_align // we know our tilt attitude
			&& !_inhibit_flow_use
			&& isTerrainEstimateValid())
		{
			// If the heading is not aligned, reset the yaw and magnetic field states
			if (!_control_status.flags.yaw_align) {
				_control_status.flags.yaw_align = resetMagHeading(_mag_lpf.getState());
			}

			// If the heading is valid and use is not inhibited , start using optical flow aiding
			if (_control_status.flags.yaw_align) {
				// set the flag and reset the fusion timeout
				_control_status.flags.opt_flow = true;
				_time_last_of_fuse = _time_last_imu;

				// if we are not using GPS or external vision aiding, then the velocity and position states and covariances need to be set
				const bool flow_aid_only = !isOtherSourceOfHorizontalAidingThan(_control_status.flags.opt_flow);
				if (flow_aid_only) {
					// TODO: Issue: First time we want to reset the optical flow velocity
					// we will use _flow_compensated_XY_rad in the resetVelocity() function,
					// but _flow_compensated_XY_rad is this zero as it gets updated for the first time below here.
					resetVelocity();
					resetHorizontalPosition();

					// align the output observer to the EKF states
					alignOutputFilter();
				}
			}

		} else if (!(_params.fusion_mode & MASK_USE_OF)) {
			_control_status.flags.opt_flow = false;
		}

		// handle the case when we have optical flow, are reliant on it, but have not been using it for an extended period
		if (isOnlyActiveSourceOfHorizontalAiding(_control_status.flags.opt_flow)) {

			bool do_reset = isTimedOut(_time_last_of_fuse, _params.reset_timeout_max);

			if (do_reset) {
				resetVelocity();
				resetHorizontalPosition();
			}
		}

		// Only fuse optical flow if valid body rate compensation data is available
		if (calcOptFlowBodyRateComp()) {

			bool flow_quality_good = (_flow_sample_delayed.quality >= _params.flow_qual_min);

			if (!flow_quality_good && !_control_status.flags.in_air) {
				// when on the ground with poor flow quality, assume zero ground relative velocity and LOS rate
				_flow_compensated_XY_rad.setZero();
			} else {
				// compensate for body motion to give a LOS rate
				_flow_compensated_XY_rad = _flow_sample_delayed.flow_xy_rad - _flow_sample_delayed.gyro_xyz.xy();
			}
		} else {
			// don't use this flow data and wait for the next data to arrive
			_flow_data_ready = false;
		}
	}

	// Wait until the midpoint of the flow sample has fallen behind the fusion time horizon
	if (_flow_data_ready && (_imu_sample_delayed.time_us > _flow_sample_delayed.time_us - uint32_t(1e6f * _flow_sample_delayed.dt) / 2)) {
		// Fuse optical flow LOS rate observations into the main filter only if height above ground has been updated recently
		// but use a relaxed time criteria to enable it to coast through bad range finder data
		if (_control_status.flags.opt_flow && isRecent(_time_last_hagl_fuse, (uint64_t)10e6)) {
			fuseOptFlow();
			_last_known_posNE = _state.pos.xy();
		}

		_flow_data_ready = false;
	}
}

void Ekf::controlGpsFusion()
{
	// Check for new GPS data that has fallen behind the fusion time horizon
	if (_gps_data_ready) {

		// Detect if coming back after significant time without GPS data
		bool gps_signal_was_lost = isTimedOut(_time_prev_gps_us, 1000000);

		// GPS yaw aiding selection logic
		if ((_params.fusion_mode & MASK_USE_GPSYAW)
				&& ISFINITE(_gps_sample_delayed.yaw)
				&& _control_status.flags.tilt_align
				&& (!_control_status.flags.gps_yaw || !_control_status.flags.yaw_align)
				&& !_gps_hgt_intermittent) {

			if (resetGpsAntYaw()) {
				// flag the yaw as aligned
				_control_status.flags.yaw_align = true;

				// turn on fusion of external vision yaw measurements and disable all other yaw fusion
				_control_status.flags.gps_yaw = true;
				_control_status.flags.ev_yaw = false;
				_control_status.flags.mag_dec = false;

				stopMagHdgFusion();
				stopMag3DFusion();

				ECL_INFO_TIMESTAMPED("starting GPS yaw fusion");
			}
		}

		// fuse the yaw observation
		if (_control_status.flags.gps_yaw) {
			fuseGpsAntYaw();
		}

		// Determine if we should use GPS aiding for velocity and horizontal position
		// To start using GPS we need angular alignment completed, the local NED origin set and GPS data that has not failed checks recently
		bool gps_checks_passing = isTimedOut(_last_gps_fail_us, (uint64_t)5e6);
		bool gps_checks_failing = isTimedOut(_last_gps_pass_us, (uint64_t)5e6);
		if ((_params.fusion_mode & MASK_USE_GPS) && !_control_status.flags.gps) {
			if (_control_status.flags.tilt_align && _NED_origin_initialised && gps_checks_passing) {
				// If the heading is not aligned, reset the yaw and magnetic field states
				// Do not use external vision for yaw if using GPS because yaw needs to be
				// defined relative to an NED reference frame
				const bool want_to_reset_mag_heading = !_control_status.flags.yaw_align ||
								       _control_status.flags.ev_yaw ||
								       _mag_inhibit_yaw_reset_req;
				if (want_to_reset_mag_heading && canResetMagHeading()) {
					_control_status.flags.ev_yaw = false;
					_control_status.flags.yaw_align = resetMagHeading(_mag_lpf.getState());
					// Handle the special case where we have not been constraining yaw drift or learning yaw bias due
					// to assumed invalid mag field associated with indoor operation with a downwards looking flow sensor.
					if (_mag_inhibit_yaw_reset_req) {
						_mag_inhibit_yaw_reset_req = false;
						// Zero the yaw bias covariance and set the variance to the initial alignment uncertainty
						P.uncorrelateCovarianceSetVariance<1>(12, sq(_params.switch_on_gyro_bias * FILTER_UPDATE_PERIOD_S));
					}
				}

				// If the heading is valid start using gps aiding
				if (_control_status.flags.yaw_align) {
					// if we are not already aiding with optical flow, then we need to reset the position and velocity
					// otherwise we only need to reset the position
					_control_status.flags.gps = true;

					if (!_control_status.flags.opt_flow) {
						if (!resetHorizontalPosition() || !resetVelocity()) {
							_control_status.flags.gps = false;

						}

					} else if (!resetHorizontalPosition()) {
						_control_status.flags.gps = false;

					}

					if (_control_status.flags.gps) {
						ECL_INFO_TIMESTAMPED("starting GPS fusion");
						_time_last_gps = _time_last_imu;
					}
				}
			}

		}  else if (!(_params.fusion_mode & MASK_USE_GPS)) {
			_control_status.flags.gps = false;

		}

		// Handle the case where we are using GPS and another source of aiding and GPS is failing checks
		if (_control_status.flags.gps && gps_checks_failing && isOtherSourceOfHorizontalAidingThan(_control_status.flags.gps)) {
			stopGpsFusion();
			// Reset position state to external vision if we are going to use absolute values
			if (_control_status.flags.ev_pos && !(_params.fusion_mode & MASK_ROTATE_EV)) {
				resetHorizontalPosition();
			}
			ECL_WARN_TIMESTAMPED("GPS quality poor - stopping use");
		}

		// handle case where we are not currently using GPS, but need to align yaw angle using EKF-GSF before
		// we can start using GPS
		bool align_yaw_using_gsf = !_control_status.flags.gps && _do_ekfgsf_yaw_reset && isTimedOut(_ekfgsf_yaw_reset_time, 5000000);
		if (align_yaw_using_gsf) {
			if (resetYawToEKFGSF()) {
				_ekfgsf_yaw_reset_time = _time_last_imu;
				_do_ekfgsf_yaw_reset = false;
			}
		}

		// handle the case when we now have GPS, but have not been fusing it for an extended period
		if (_control_status.flags.gps) {
			// We are relying on aiding to constrain drift so after a specified time
			// with no aiding we need to do something
			bool do_vel_pos_reset = isTimedOut(_time_last_hor_pos_fuse, _params.reset_timeout_max)
					&& isTimedOut(_time_last_delpos_fuse, _params.reset_timeout_max)
					&& isTimedOut(_time_last_hor_vel_fuse, _params.reset_timeout_max)
					&& isTimedOut(_time_last_of_fuse, _params.reset_timeout_max);

			// We haven't had an absolute position fix for a longer time so need to do something
			do_vel_pos_reset = do_vel_pos_reset || isTimedOut(_time_last_hor_pos_fuse, 2 * _params.reset_timeout_max);

			/* Logic controlling the reset of navigation filter yaw to the EKF-GSF estimate to recover from loss of
			   navigation casued by a bad yaw estimate.

			   A rapid reset to the EKF-GSF estimate is performed after a recent takeoff if horizontal velocity
			   innovation checks fail. This enables recovery from a bad yaw estimate. After 30 seconds from takeoff,
			   different test criteria are used that take longer to trigger and reduce false positives. A reset is
			   not performed if the fault condition was present before flight to prevent triggering due to GPS glitches
			   or other sensor errors.

			   The yaw reset to the EKF-GSF estimate can be requested externally at any time during flight.

			   The total number of resets allowed per boot cycle is limited.

			   The minimum time interval between resets to the EKF-GSF estimate is limited to allow the EKF-GSF time
			   to improve its estimate if the previous reset was not successful.

			   A reset is not performed when getting GPS back after a significant period of no data because the timeout
			   could have been caused by bad GPS.
			*/

			if (!_control_status.flags.in_air) {
				_time_last_on_ground_us = _time_last_imu;
			}

			const bool recent_takeoff_nav_failure = _control_status.flags.in_air &&
								!isTimedOut(_time_last_on_ground_us, 30000000) &&
								isTimedOut(_time_last_hor_vel_fuse, _params.EKFGSF_reset_delay) &&
								(_time_last_hor_vel_fuse > _time_last_on_ground_us);

			const bool inflight_nav_failure = _control_status.flags.in_air &&
							  do_vel_pos_reset &&
							  (_time_last_hor_vel_fuse > _time_last_on_ground_us) &&
							  (_time_last_hor_pos_fuse > _time_last_on_ground_us);

			const bool do_yaw_vel_pos_reset = (_do_ekfgsf_yaw_reset || recent_takeoff_nav_failure || inflight_nav_failure) &&
							  _ekfgsf_yaw_reset_count < _params.EKFGSF_reset_count_limit &&
							  isTimedOut(_ekfgsf_yaw_reset_time, 5000000) &&
							  !gps_signal_was_lost;

			if (do_yaw_vel_pos_reset) {
				if (resetYawToEKFGSF()) {
					_ekfgsf_yaw_reset_time = _time_last_imu;
					_do_ekfgsf_yaw_reset = false;
					_ekfgsf_yaw_reset_count++;

					// Reset the timeout counters
					_time_last_hor_pos_fuse = _time_last_imu;
					_time_last_delpos_fuse = _time_last_imu;
					_time_last_hor_vel_fuse = _time_last_imu;
					_time_last_of_fuse = _time_last_imu;
				}

			} else if (do_vel_pos_reset) {
				// use GPS velocity data to check and correct yaw angle if a FW vehicle
				if (_control_status.flags.fixed_wing && _control_status.flags.in_air) {
					// if flying a fixed wing aircraft, do a complete reset that includes yaw
					_control_status.flags.mag_aligned_in_flight = realignYawGPS();
				}

				resetVelocity();
				resetHorizontalPosition();
				_velpos_reset_request = false;
				ECL_WARN_TIMESTAMPED("GPS fusion timeout - reset to GPS");

				// Reset the timeout counters
				_time_last_hor_pos_fuse = _time_last_imu;
				_time_last_hor_vel_fuse = _time_last_imu;
			}
		}

		// Only use GPS data for position and velocity aiding if enabled
		if (_control_status.flags.gps) {

			Vector2f gps_vel_innov_gates; // [horizontal vertical]
			Vector2f gps_pos_innov_gates; // [horizontal vertical]
			Vector3f gps_vel_obs_var;
			Vector3f gps_pos_obs_var;

			// correct velocity for offset relative to IMU
			const Vector3f pos_offset_body = _params.gps_pos_body - _params.imu_pos_body;
			const Vector3f vel_offset_body = _ang_rate_delayed_raw % pos_offset_body;
			const Vector3f vel_offset_earth = _R_to_earth * vel_offset_body;
			_gps_sample_delayed.vel -= vel_offset_earth;

			// correct position and height for offset relative to IMU
			const Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
			_gps_sample_delayed.pos -= pos_offset_earth.xy();
			_gps_sample_delayed.hgt += pos_offset_earth(2);

			const float lower_limit = fmaxf(_params.gps_pos_noise, 0.01f);

			if (isOtherSourceOfHorizontalAidingThan(_control_status.flags.gps)) {
				// if we are using other sources of aiding, then relax the upper observation
				// noise limit which prevents bad GPS perturbing the position estimate
				gps_pos_obs_var(0) = gps_pos_obs_var(1) = sq(fmaxf(_gps_sample_delayed.hacc, lower_limit));

			} else {
				// if we are not using another source of aiding, then we are reliant on the GPS
				// observations to constrain attitude errors and must limit the observation noise value.
				float upper_limit = fmaxf(_params.pos_noaid_noise, lower_limit);
				gps_pos_obs_var(0) = gps_pos_obs_var(1) = sq(math::constrain(_gps_sample_delayed.hacc, lower_limit, upper_limit));
			}

			gps_vel_obs_var.setAll(sq(fmaxf(_gps_sample_delayed.sacc, _params.gps_vel_noise)));
			gps_vel_obs_var(2) = sq(1.5f) * gps_vel_obs_var(2);

			// calculate innovations
			_gps_vel_innov = _state.vel - _gps_sample_delayed.vel;
			_gps_pos_innov.xy() = Vector2f(_state.pos) - _gps_sample_delayed.pos;

			// set innovation gate size
			gps_pos_innov_gates(0) = fmaxf(_params.gps_pos_innov_gate, 1.0f);
			gps_vel_innov_gates(0) = gps_vel_innov_gates(1) = fmaxf(_params.gps_vel_innov_gate, 1.0f);

			// fuse GPS measurement
			fuseHorizontalVelocity(_gps_vel_innov, gps_vel_innov_gates,gps_vel_obs_var, _gps_vel_innov_var, _gps_vel_test_ratio);
			fuseVerticalVelocity(_gps_vel_innov, gps_vel_innov_gates, gps_vel_obs_var, _gps_vel_innov_var, _gps_vel_test_ratio);
			fuseHorizontalPosition(_gps_pos_innov, gps_pos_innov_gates, gps_pos_obs_var, _gps_pos_innov_var, _gps_pos_test_ratio);
		}

	} else if (_control_status.flags.gps && (_imu_sample_delayed.time_us - _gps_sample_delayed.time_us > (uint64_t)10e6)) {
		stopGpsFusion();
		ECL_WARN_TIMESTAMPED("GPS data stopped");
	}  else if (_control_status.flags.gps && (_imu_sample_delayed.time_us - _gps_sample_delayed.time_us > (uint64_t)1e6) && isOtherSourceOfHorizontalAidingThan(_control_status.flags.gps)) {
		// Handle the case where we are fusing another position source along GPS,
		// stop waiting for GPS after 1 s of lost signal
		stopGpsFusion();
		ECL_WARN_TIMESTAMPED("GPS data stopped, using only EV or OF");
	}
}

void Ekf::controlHeightSensorTimeouts()
{
	/*
	 * Handle the case where we have not fused height measurements recently and
	 * uncertainty exceeds the max allowable. Reset using the best available height
	 * measurement source, continue using it after the reset and declare the current
	 * source failed if we have switched.
	*/

	checkVerticalAccelerationHealth();

	// check if height is continuously failing because of accel errors
	bool continuous_bad_accel_hgt = isTimedOut(_time_good_vert_accel, (uint64_t)_params.bad_acc_reset_delay_us);

	// check if height has been inertial deadreckoning for too long
	bool hgt_fusion_timeout = isTimedOut(_time_last_hgt_fuse, (uint64_t)5e6);

	if (hgt_fusion_timeout || continuous_bad_accel_hgt) {

		bool request_height_reset = false;
		const char* failing_height_source = nullptr;
		const char* new_height_source = nullptr;

		if (_control_status.flags.baro_hgt) {
			// check if GPS height is available
			const gpsSample &gps_init = _gps_buffer.get_newest();
			const bool gps_hgt_accurate = (gps_init.vacc < _params.req_vacc);

			// check for inertial sensing errors in the last BADACC_PROBATION seconds
			const bool prev_bad_vert_accel = isRecent(_time_bad_vert_accel, BADACC_PROBATION);

			// reset to GPS if adequate GPS data is available and the timeout cannot be blamed on IMU data
			const bool reset_to_gps = !_gps_hgt_intermittent &&
					    ((gps_hgt_accurate && !prev_bad_vert_accel) || _baro_hgt_faulty);

			if (reset_to_gps) {
				// set height sensor health
				_baro_hgt_faulty = true;

				startGpsHgtFusion();

				request_height_reset = true;
				failing_height_source = "baro";
				new_height_source = "gps";

			} else if (!_baro_hgt_faulty) {
				request_height_reset = true;
				failing_height_source = "baro";
				new_height_source = "baro";
			}

		} else if (_control_status.flags.gps_hgt) {
			// check if GPS height is available
			const gpsSample &gps_init = _gps_buffer.get_newest();
			const bool gps_hgt_accurate = (gps_init.vacc < _params.req_vacc);

			// check the baro height source for consistency and freshness
			const baroSample &baro_init = _baro_buffer.get_newest();
			const float baro_innov = _state.pos(2) - (_hgt_sensor_offset - baro_init.hgt + _baro_hgt_offset);
			const bool baro_data_consistent = fabsf(baro_innov) < (sq(_params.baro_noise) + P(9,9)) * sq(_params.baro_innov_gate);

			// if baro data is acceptable and GPS data is inaccurate, reset height to baro
			const bool reset_to_baro = !_baro_hgt_faulty &&
						   ((baro_data_consistent && !gps_hgt_accurate) ||
						     _gps_hgt_intermittent);

			if (reset_to_baro) {
				startBaroHgtFusion();

				request_height_reset = true;
				failing_height_source = "gps";
				new_height_source = "baro";

			} else if (!_gps_hgt_intermittent) {
				request_height_reset = true;
				failing_height_source = "gps";
				new_height_source = "gps";
			}

		} else if (_control_status.flags.rng_hgt) {

			if (_range_sensor.isHealthy()) {
				request_height_reset = true;
				failing_height_source = "rng";
				new_height_source = "rng";

			} else if (!_baro_hgt_faulty) {
				startBaroHgtFusion();

				request_height_reset = true;
				failing_height_source = "rng";
				new_height_source = "baro";
			}

		} else if (_control_status.flags.ev_hgt) {
			// check if vision data is available
			const extVisionSample &ev_init = _ext_vision_buffer.get_newest();
			const bool ev_data_available = isRecent(ev_init.time_us, 2 * EV_MAX_INTERVAL);

			if (ev_data_available) {
				request_height_reset = true;
				failing_height_source = "ev";
				new_height_source = "ev";

			} else if (!_baro_hgt_faulty) {
				startBaroHgtFusion();

				request_height_reset = true;
				failing_height_source = "ev";
				new_height_source = "baro";
			}
		}

		if (failing_height_source && new_height_source) {
			ECL_WARN("%s hgt timeout - reset to %s", failing_height_source, new_height_source);
		}

		// Reset vertical position and velocity states to the last measurement
		if (request_height_reset) {
			resetHeight();
			// Reset the timout timer
			_time_last_hgt_fuse = _time_last_imu;
		}
	}
}

void Ekf::checkVerticalAccelerationHealth()
{
	// Check for IMU accelerometer vibration induced clipping as evidenced by the vertical
	// innovations being positive and not stale.
	// Clipping causes the average accel reading to move towards zero which makes the INS
	// think it is falling and produces positive vertical innovations

	const float var_product_lim = sq(_params.vert_innov_test_lim) * sq(_params.vert_innov_test_lim);
	const bool is_fusing_gps_vel = !_gps_hgt_intermittent;
	const bool is_fusing_baro_alt = _control_status.flags.baro_hgt && !_baro_hgt_faulty;
	const bool are_vertical_pos_and_vel_independant = is_fusing_gps_vel && is_fusing_baro_alt; // TODO: should we add range hgt here?
	const float pos_vel_innov_product = _gps_pos_innov(2) * fmaxf(fabsf(_gps_vel_innov(2)),fabsf(_ev_vel_innov(2)));
	const float pos_vel_innov_var_product = _gps_pos_innov_var(2) * fmaxf(fabsf(_gps_vel_innov_var(2)),fabsf(_ev_vel_innov_var(2)));
	const bool are_pos_vel_sensor_in_agreement = sq(pos_vel_innov_product) > var_product_lim * (pos_vel_innov_var_product);

	// A positive innovation indicates that the inertial nav thinks it is falling
	// This is caused by average of the Z accelerometer being 0, due to clipping
	const bool is_inertial_nav_falling = _gps_vel_innov(2) > 0.0f || _ev_vel_innov(2) > 0.0f;

	const bool bad_vert_accel = are_vertical_pos_and_vel_independant &&
			      are_pos_vel_sensor_in_agreement &&
			      is_inertial_nav_falling;

	if (bad_vert_accel) {
		_time_bad_vert_accel =  _time_last_imu;

	} else {
		_time_good_vert_accel = _time_last_imu;
	}

	// declare a bad vertical acceleration measurement and make the declaration persist
	// for a minimum of BADACC_PROBATION seconds
	if (_bad_vert_accel_detected) {
		_bad_vert_accel_detected = isRecent(_time_bad_vert_accel, BADACC_PROBATION);

	} else {
		_bad_vert_accel_detected = bad_vert_accel;
	}
}

void Ekf::controlHeightFusion()
{
	checkRangeAidSuitability();
	const bool do_range_aid = (_params.range_aid == 1) && isRangeAidSuitable();

	bool fuse_height = false;

	switch (_params.vdist_sensor_type) {
	default:
		ECL_ERR("Invalid hgt mode: %d", _params.vdist_sensor_type);

	// FALLTHROUGH
	case VDIST_SENSOR_BARO:
		if (do_range_aid && _range_sensor.isDataHealthy()) {
			setControlRangeHeight();
			fuse_height = true;

			// we have just switched to using range finder, calculate height sensor offset such that current
			// measurement matches our current height estimate
			if (_control_status_prev.flags.rng_hgt != _control_status.flags.rng_hgt) {
				_hgt_sensor_offset = _terrain_vpos;
			}

		} else if (!do_range_aid && _baro_data_ready && !_baro_hgt_faulty) {
			startBaroHgtFusion();
			fuse_height = true;

		} else if (_control_status.flags.gps_hgt && _gps_data_ready && !_gps_hgt_intermittent) {
			// switch to gps if there was a reset to gps
			fuse_height = true;

			// we have just switched to using gps height, calculate height sensor offset such that current
			// measurement matches our current height estimate
			if (_control_status_prev.flags.gps_hgt != _control_status.flags.gps_hgt) {
				_hgt_sensor_offset = _gps_sample_delayed.hgt - _gps_alt_ref + _state.pos(2);
			}
		}

		break;

	case VDIST_SENSOR_RANGE:
		if (_range_sensor.isDataHealthy()) {
			setControlRangeHeight();
			fuse_height = true;

			if (_control_status_prev.flags.rng_hgt != _control_status.flags.rng_hgt) {
				// we have just switched to using range finder, calculate height sensor offset such that current
				// measurement matches our current height estimate
				// use the parameter rng_gnd_clearance if on ground to avoid a noisy offset initialization (e.g. sonar)
				if (_control_status.flags.in_air && isTerrainEstimateValid()) {
					_hgt_sensor_offset = _terrain_vpos;

				} else if (_control_status.flags.in_air) {
					_hgt_sensor_offset = _range_sensor.getDistBottom() + _state.pos(2);

				} else {
					_hgt_sensor_offset = _params.rng_gnd_clearance;
				}
			}

		} else if (_baro_data_ready && !_baro_hgt_faulty) {
			startBaroHgtFusion();
			fuse_height = true;
		}

		break;

	case VDIST_SENSOR_GPS:

		// NOTE: emergency fallback due to extended loss of currently selected sensor data or failure
		// to pass innovation cinsistency checks is handled elsewhere in Ekf::controlHeightSensorTimeouts.
		// Do switching between GPS and rangefinder if using range finder as a height source when close
		// to ground and moving slowly. Also handle switch back from emergency Baro sensor when GPS recovers.
		if (!_control_status_prev.flags.rng_hgt && do_range_aid && _range_sensor.isDataHealthy()) {
			setControlRangeHeight();

			// we have just switched to using range finder, calculate height sensor offset such that current
			// measurement matches our current height estimate
			_hgt_sensor_offset = _terrain_vpos;

		} else if (_control_status_prev.flags.rng_hgt && !do_range_aid) {
			// must stop using range finder so find another sensor now
			if (!_gps_hgt_intermittent && _gps_checks_passed) {
				// GPS quality OK
				startGpsHgtFusion();
			} else if (!_baro_hgt_faulty) {
				// Use baro as a fallback
				startBaroHgtFusion();
			}
		} else if (_control_status.flags.baro_hgt && !do_range_aid && !_gps_hgt_intermittent && _gps_checks_passed) {
			// In baro fallback mode and GPS has recovered so start using it
			startGpsHgtFusion();
		}
		if (_control_status.flags.gps_hgt && _gps_data_ready) {
			fuse_height = true;
		} else if (_control_status.flags.rng_hgt && _range_sensor.isDataHealthy()) {
			fuse_height = true;
		} else if (_control_status.flags.baro_hgt && _baro_data_ready && !_baro_hgt_faulty) {
			fuse_height = true;
		}
		break;

	case VDIST_SENSOR_EV:

		// don't start using EV data unless data is arriving frequently
		if (!_control_status.flags.ev_hgt && isRecent(_time_last_ext_vision, 2 * EV_MAX_INTERVAL)) {
			fuse_height = true;
			setControlEVHeight();
			resetHeight();
		}

		if (_control_status.flags.baro_hgt && _baro_data_ready && !_baro_hgt_faulty) {
			// switch to baro if there was a reset to baro
			fuse_height = true;
		}

		// determine if we should use the vertical position observation
		if (_control_status.flags.ev_hgt) {
			fuse_height = true;
		}

		break;
	}

	updateBaroHgtOffset();

	if (isTimedOut(_time_last_hgt_fuse, 2 * RNG_MAX_INTERVAL) && _control_status.flags.rng_hgt
	    && (!_range_sensor.isDataHealthy())) {

		// If we are supposed to be using range finder data as the primary height sensor, have missed or rejected measurements
		// and are on the ground, then synthesise a measurement at the expected on ground value
		if (!_control_status.flags.in_air) {
			_range_sensor.setRange(_params.rng_gnd_clearance);
			_range_sensor.setDataReadiness(true);
			_range_sensor.setValidity(true); // bypass the checks
		}

		fuse_height = true;
	}

	if (fuse_height) {
		if (_control_status.flags.baro_hgt) {
			Vector2f baro_hgt_innov_gate;
			Vector3f baro_hgt_obs_var;

			// vertical position innovation - baro measurement has opposite sign to earth z axis
			_baro_hgt_innov(2) = _state.pos(2) + _baro_sample_delayed.hgt - _baro_hgt_offset;
			// observation variance - user parameter defined
			baro_hgt_obs_var(2) = sq(fmaxf(_params.baro_noise, 0.01f));
			// innovation gate size
			baro_hgt_innov_gate(1) = fmaxf(_params.baro_innov_gate, 1.0f);

			// Compensate for positive static pressure transients (negative vertical position innovations)
			// caused by rotor wash ground interaction by applying a temporary deadzone to baro innovations.
			float deadzone_start = 0.0f;
			float deadzone_end = deadzone_start + _params.gnd_effect_deadzone;

			if (_control_status.flags.gnd_effect) {
				if (_baro_hgt_innov(2) < -deadzone_start) {
					if (_baro_hgt_innov(2) <= -deadzone_end) {
						_baro_hgt_innov(2) += deadzone_end;

					} else {
						_baro_hgt_innov(2) = -deadzone_start;
					}
				}
			}
			// fuse height information
			fuseVerticalPosition(_baro_hgt_innov,baro_hgt_innov_gate,
				baro_hgt_obs_var, _baro_hgt_innov_var,_baro_hgt_test_ratio);

		} else if (_control_status.flags.gps_hgt) {
			Vector2f gps_hgt_innov_gate;
			Vector3f gps_hgt_obs_var;
			// vertical position innovation - gps measurement has opposite sign to earth z axis
			_gps_pos_innov(2) = _state.pos(2) + _gps_sample_delayed.hgt - _gps_alt_ref - _hgt_sensor_offset;
			// observation variance - receiver defined and parameter limited
			// use scaled horizontal position accuracy assuming typical ratio of VDOP/HDOP
			const float lower_limit = fmaxf(_params.gps_pos_noise, 0.01f);
			const float upper_limit = fmaxf(_params.pos_noaid_noise, lower_limit);
			gps_hgt_obs_var(2) = sq(1.5f * math::constrain(_gps_sample_delayed.vacc, lower_limit, upper_limit));
			// innovation gate size
			gps_hgt_innov_gate(1) = fmaxf(_params.baro_innov_gate, 1.0f);
			// fuse height information
			fuseVerticalPosition(_gps_pos_innov,gps_hgt_innov_gate,
				gps_hgt_obs_var, _gps_pos_innov_var,_gps_pos_test_ratio);

		} else if (_control_status.flags.rng_hgt) {
			Vector2f rng_hgt_innov_gate;
			Vector3f rng_hgt_obs_var;
			// use range finder with tilt correction
			_rng_hgt_innov(2) = _state.pos(2) - (-math::max(_range_sensor.getDistBottom(),
							 _params.rng_gnd_clearance)) - _hgt_sensor_offset;
			// observation variance - user parameter defined
			rng_hgt_obs_var(2) = fmaxf(sq(_params.range_noise)
						   + sq(_params.range_noise_scaler * _range_sensor.getDistBottom()), 0.01f);
			// innovation gate size
			rng_hgt_innov_gate(1) = fmaxf(_params.range_innov_gate, 1.0f);
			// fuse height information
			fuseVerticalPosition(_rng_hgt_innov,rng_hgt_innov_gate,
				rng_hgt_obs_var, _rng_hgt_innov_var,_rng_hgt_test_ratio);

		} else if (_control_status.flags.ev_hgt) {
			Vector2f ev_hgt_innov_gate;
			Vector3f ev_hgt_obs_var;
			// calculate the innovation assuming the external vision observation is in local NED frame
			_ev_pos_innov(2) = _state.pos(2) - _ev_sample_delayed.pos(2);
			// observation variance - defined externally
			ev_hgt_obs_var(2) = fmaxf(_ev_sample_delayed.posVar(2), sq(0.01f));
			// innovation gate size
			ev_hgt_innov_gate(1) = fmaxf(_params.ev_pos_innov_gate, 1.0f);
			// fuse height information
			fuseVerticalPosition(_ev_pos_innov,ev_hgt_innov_gate,
				ev_hgt_obs_var, _ev_pos_innov_var,_ev_pos_test_ratio);
		}
	}
}

void Ekf::checkRangeAidSuitability()
{
	if (_control_status.flags.in_air
	    && _range_sensor.isHealthy()
	    && isTerrainEstimateValid()
	    && isHorizontalAidingActive()) {
		// check if we can use range finder measurements to estimate height, use hysteresis to avoid rapid switching
		// Note that the 0.7 coefficients and the innovation check are arbitrary values but work well in practice
		const bool is_in_range = _is_range_aid_suitable
					 ? (_terrain_vpos - _state.pos(2) < _params.max_hagl_for_range_aid)
					 : (_terrain_vpos - _state.pos(2) < _params.max_hagl_for_range_aid * 0.7f);

		const float ground_vel = sqrtf(_state.vel(0) * _state.vel(0) + _state.vel(1) * _state.vel(1));
		const bool is_below_max_speed = _is_range_aid_suitable
						? ground_vel < _params.max_vel_for_range_aid
						: ground_vel < _params.max_vel_for_range_aid * 0.7f;

		const bool is_hagl_stable = _is_range_aid_suitable
					    ? ((_hagl_innov * _hagl_innov / (sq(_params.range_aid_innov_gate) * _hagl_innov_var)) < 1.0f)
					    : ((_hagl_innov * _hagl_innov / (sq(_params.range_aid_innov_gate) * _hagl_innov_var)) < 0.01f);

		_is_range_aid_suitable = is_in_range && is_below_max_speed && is_hagl_stable;

	} else {
		_is_range_aid_suitable = false;
	}
}

void Ekf::controlAirDataFusion()
{
	// control activation and initialisation/reset of wind states required for airspeed fusion

	// If both airspeed and sideslip fusion have timed out and we are not using a drag observation model then we no longer have valid wind estimates
	const bool airspeed_timed_out = isTimedOut(_time_last_arsp_fuse, (uint64_t)10e6);
	const bool sideslip_timed_out = isTimedOut(_time_last_beta_fuse, (uint64_t)10e6);

	if (_control_status.flags.wind && airspeed_timed_out && sideslip_timed_out && !(_params.fusion_mode & MASK_USE_DRAG)) {
		_control_status.flags.wind = false;
	}

	if (_control_status.flags.fuse_aspd && airspeed_timed_out) {
		_control_status.flags.fuse_aspd = false;
	}

	// Always try to fuse airspeed data if available and we are in flight
	if (_tas_data_ready && _control_status.flags.in_air) {
		// always fuse airsped data if we are flying and data is present
		if (!_control_status.flags.fuse_aspd) {
			_control_status.flags.fuse_aspd = true;
		}

		// If starting wind state estimation, reset the wind states and covariances before fusing any data
		if (!_control_status.flags.wind) {
			// activate the wind states
			_control_status.flags.wind = true;
			// reset the timout timer to prevent repeated resets
			_time_last_arsp_fuse = _time_last_imu;
			_time_last_beta_fuse = _time_last_imu;
			// reset the wind speed states and corresponding covariances
			resetWindStates();
			resetWindCovariance();
		}

		fuseAirspeed();
	}
}

void Ekf::controlBetaFusion()
{
	// control activation and initialisation/reset of wind states required for synthetic sideslip fusion fusion

	// If both airspeed and sideslip fusion have timed out and we are not using a drag observation model then we no longer have valid wind estimates
	const bool sideslip_timed_out = isTimedOut(_time_last_beta_fuse, (uint64_t)10e6);
	const bool airspeed_timed_out = isTimedOut(_time_last_arsp_fuse, (uint64_t)10e6);

	if (_control_status.flags.wind && airspeed_timed_out && sideslip_timed_out && !(_params.fusion_mode & MASK_USE_DRAG)) {
		_control_status.flags.wind = false;
	}

	// Perform synthetic sideslip fusion when in-air and sideslip fuson had been enabled externally in addition to the following criteria:

	// Sufficient time has lapsed sice the last fusion
	bool beta_fusion_time_triggered = isTimedOut(_time_last_beta_fuse, _params.beta_avg_ft_us);

	if (beta_fusion_time_triggered && _control_status.flags.fuse_beta && _control_status.flags.in_air) {
		// If starting wind state estimation, reset the wind states and covariances before fusing any data
		if (!_control_status.flags.wind) {
			// activate the wind states
			_control_status.flags.wind = true;
			// reset the timeout timers to prevent repeated resets
			_time_last_beta_fuse = _time_last_imu;
			_time_last_arsp_fuse = _time_last_imu;
			// reset the wind speed states and corresponding covariances
			resetWindStates();
			resetWindCovariance();
		}

		fuseSideslip();
	}
}

void Ekf::controlDragFusion()
{
	if (_params.fusion_mode & MASK_USE_DRAG) {
		if (_control_status.flags.in_air
				&& !_mag_inhibit_yaw_reset_req) {
			if (!_control_status.flags.wind) {
				// reset the wind states and covariances when starting drag accel fusion
				_control_status.flags.wind = true;
				resetWindStates();
				resetWindCovariance();

			} else if (_drag_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_drag_sample_delayed)) {
				fuseDrag();
			}

		} else {
			_control_status.flags.wind = false;
		}
	}
}

void Ekf::controlFakePosFusion()
{
	// if we aren't doing any aiding, fake position measurements at the last known position to constrain drift
	// Coincide fake measurements with baro data for efficiency with a minimum fusion rate of 5Hz

	if (!isHorizontalAidingActive()
	    && !(_control_status.flags.fuse_aspd && _control_status.flags.fuse_beta)) {

		// We now need to use a synthetic position observation to prevent unconstrained drift of the INS states.
		_using_synthetic_position = true;

		// Fuse synthetic position observations every 200msec
		if (isTimedOut(_time_last_fake_pos, (uint64_t)2e5)) {

			Vector3f fake_pos_obs_var;

			// Reset position and velocity states if we re-commence this aiding method
			if (isTimedOut(_time_last_fake_pos, (uint64_t)4e5)) {
				resetHorizontalPosition();
				resetVelocity();
				_fuse_hpos_as_odom = false;

				if (_time_last_fake_pos != 0) {
					ECL_WARN_TIMESTAMPED("stopping navigation");
				}

			}
			_time_last_fake_pos = _time_last_imu;

			if (_control_status.flags.in_air && _control_status.flags.tilt_align) {
				fake_pos_obs_var(0) = fake_pos_obs_var(1) = sq(fmaxf(_params.pos_noaid_noise, _params.gps_pos_noise));

			} else {
				fake_pos_obs_var(0) = fake_pos_obs_var(1) = sq(0.5f);
			}

			_gps_pos_innov.xy() = Vector2f(_state.pos) - _last_known_posNE;

			// glitch protection is not required so set gate to a large value
			const Vector2f fake_pos_innov_gate(100.0f, 100.0f);

			fuseHorizontalPosition(_gps_pos_innov, fake_pos_innov_gate, fake_pos_obs_var,
						_gps_pos_innov_var, _gps_pos_test_ratio);
		}

	} else {
		_using_synthetic_position = false;
	}

}

void Ekf::controlAuxVelFusion()
{
	const bool data_ready = _auxvel_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_auxvel_sample_delayed);

	if (data_ready && isHorizontalAidingActive()) {

		const Vector2f aux_vel_innov_gate(_params.auxvel_gate, _params.auxvel_gate);

		_aux_vel_innov = _state.vel - _auxvel_sample_delayed.vel;

		fuseHorizontalVelocity(_aux_vel_innov, aux_vel_innov_gate, _auxvel_sample_delayed.velVar,
				_aux_vel_innov_var, _aux_vel_test_ratio);

		// Can be enabled after bit for this is added to EKF_AID_MASK
		// fuseVerticalVelocity(_aux_vel_innov, aux_vel_innov_gate, _auxvel_sample_delayed.velVar,
		//		_aux_vel_innov_var, _aux_vel_test_ratio);

	}
}
